For as long as food has been cooked, the Maillard reaction has played an important role in improving the appearance and taste of foods. Controlling Maillard reactions has been a central and major challenge in food industry, because aroma, taste and sensorial properties as well as colour are all strongly affected by Maillard chemistry, particularly in traditional processes such as the roasting of coffee and cocoa beans, the baking of bread and cakes, the toasting of cereals and the cooking of meat.
Maillard reaction technology is used by the flavour industry for the production of so-called process or reaction flavours. Process flavours are complex aroma building blocks, which provide similar aroma and taste properties as thermally treated foodstuffs such as cooked meat, chocolate, coffee, caramel, popcorn and bread. Additionally, they can be combined with other flavour ingredients to impart flavour enhancement and/or specific flavour notes in the applications in which they are used.
During the Maillard reaction a wide range of reaction products is formed with significant importance for amongst others the taste of foods. The chemistry underlying the Maillard reaction is very complex. It involves not one reaction pathway but a whole array of various reaction cascades. The Maillard reaction is most commonly known as the reaction of an amino group of e.g. an amino acid, peptide or protein, with the keto group of a sugar, followed by other, more complex changes which result eventually in the formation of a variety of volatiles and non-volatiles.
It is known, for example, that reaction products obtained by heating a mixture of sulphur-containing amino acids and reducing sugar, have a characteristic flavour similar to roasted or cooked meat to some extent. These Maillard reaction products can suitably be employed as flavouring material for foodstuffs.
Though the understanding of the reaction by food technologists is advancing steadily, the Maillard reaction is notoriously difficult to control. The rate of the Maillard reaction and the nature of the products formed are not only dependant on the reactants present but are also greatly influenced by the reaction conditions. These include the pH and water activity, the presence of oxygen and metals, the temperature-time combination during heating and the presence of reaction inhibitors (like sulphur dioxide). These factors together determine the development of the Maillard reaction during processing, thereby having a high impact on both intensity and quality of the obtained process flavour.
Generally speaking, the Maillard reaction is most effective in generating flavour components when the water activity is low. That is one reason why the outer crust of meat and bread or roasted coffee beans do contain high concentrations of Maillard reaction products in the form of volatile molecules (aroma) and non-volatile molecules (colour and taste).
In order to make Maillard flavours with a broad range of aroma compounds and to do so as efficiently as possible, i.e. in higher yields and/or at a higher reaction rate, several methods using liquid phases with low water activity have been proposed.
In U.S. Pat. No. 4,879,130 a method of producing a flavouring agent is described, wherein a paste-like mixture prepared from 70-95 wt % of a source of free amino acids, 1-25 wt % of additives, including at least one reducing sugar and water, is heated and kneaded in order to plasticize it. After extrusion the plasticized mixture is further heated in order to react. After drying and cooling a flavorant is obtained.
In EP-A-1 008 305 a method for producing an aroma product is disclosed wherein saturated C16-C18 monoglycerides are added to an aqueous dispersion of amino acids, peptides or hydrolysed protein and reducing sugars and wherein the mixture is subsequently heated to obtain a micro emulsion. By continuous heating of the micro emulsion flavouring compounds develop.
In EP 0 571 031 a process for the preparation of a savoury flavour is described which comprises reacting mono and or di-methyl-3(2H)-furanone with cystein and or hydrogen sulphide. The reaction is carried out in a medium comprising an organic polar solvent such as glycerol or propylene glycol and less than 20% of water. In addition, a food acid, such as acetic acid, may be present in order to stabilize the thiols present, resulting in higher yields of one of the important meat flavour compounds. According to this document the acetic acid is added in an amount of about 41 mmol/kg.